Low occurrence of colistin-resistant Escherichia coli in faecal content of pigs in French commercial herds

We tested the susceptibility to colistin of Escherichia coli indicator strains isolated from the faecal content of pigs of various ages housed in commercial French farrow-to-finish herds. This antimicrobial had been administered to piglets during the lactating period and more frequently after weaning in most of the selected farms (13 Out Of 16). Twenty-three strains (22 from young pigs) out of the 4333 tested were classified as resistant by disk diffusion method and confirmed by MIC determination (4 to 16 mu g/ml). Our results indicate that disk diffusion method can be a valuable method for the assessment of colistin resistance and illustrate the infrequent occurrence of resistance to this antimicrobial.